1. Field of the Invention
This invention relates to a method and system for regenerating spent activated carbon to remove materials adsorbed on the activated carbon.
2. State of the Art
Generally speaking, activated carbon comprises particles of carbon which have been treated so that they are able to adsorb organic materials. It is well-known that activated carbon can be used to remove certain organic chemicals from liquid and gases. For example, activated carbon can be used to reduce pollution in certain types of wastewaters and to decolorize sugar liquors and the like. In a conventional wastewater treatment system utilizing activated carbon the wastewater is passed through a vessel filled with granules of the carbon, and pollutants are removed from the water by adsorbtion on the carbon.
After a period of use, the activated carbon becomes saturated with pollutants and thus "spent" and must be regenerated before it can be further used effectively. Conventional means for regeneration include thermal treatment of the spent carbon. In particular one patented thermal regeneration process involves the steps of drying, heating and burning. According to the thermal regeneration process taught in U.S. Pat. No. 3,153,633 to Von Dreusche, Jr. spent activated carbon is fed to a furnace of the multiple-hearth type, and dried and regnerated therein.
According to the patent, in the multiple-hearth furnace the wet, spent activated carbon is first heated in the upper part of the furnace to drive off moisture. The moisture and gases are removed from the furnace and part are discharged to the atmosphere while the remainder are transferred to the lower part of the furnace. The carbon moves downward and is heated in the lower part of the furnace by burning fuel therein. Air is introduced into the lower part of the furnace to promote combustion.
It should thus be understood that in the above-identified patented system substantial quantities of moisture are heated and driven from the carbon and then discharged to the atmosphere. It should also be understood that air contains a substantial percentage of inert gases such as nitrogen. Therefore the gases cycled from the upper to the lower part of the furnace contain a substantial quantity of inert gas.